The present invention relates to a power supplying circuit, more particularly, a control circuit for heat fixing device capable of automatically supplying a certain voltage previously determined to a load even though a specification of power supply voltage is changed
In a copying machine and a printing apparatus, a heat fixing device such as an oven fixing device and heat roll fixing device is utilized to fix a toner image transferred onto a record paper. Such a heat fixing device utilizes, for example, a halogen lamp having a rated output of 1 KW as a heat source, and a toner image is fused and fixed onto the record paper with the use of heat emitted therefrom. The halogen lamp for use in the heat fixing device has a load resistance value fixed for the rated power supply voltage, so that if the input voltage of the lamp is changed or fluctuated with time, the power consumption becomes changed While the voltage of commercial power source is different each country, so that when the products for the apparatus are exported to many country, the specification of the halogen lamp or power source circuit must be adapted to that of the commercial power source voltage of each country. In the conventional copying machine and the printing apparatus, therefore, every commercial power source voltage of each country, respective halogen lamps having different load resistance values are utilized, or a large power controlling transformer is incorporated in the power circuit to step down the commercial power source to the rated voltage of lamp.
As described above, in the method of in corporating the halogen lamp having different specifications into the heat fixing device every different commercial power voltage, halogen lamps having various kinds of specifications must be supplied to the production line and administrated, so that the management of production steps becomes difficult and complicated While, in the method of incorporating the control transformer in the power circuit, to step down the commercial power voltage to the rated voltage of lamp, and of applying the thus obtained rated voltage to the halogen lamp, even if the commercial power voltage is changed, the halogen lamp having same specifications can be used, but production cost becomes high, because of high and large power controlling transformer. Such a defect generates also in case of applying power voltage to the halogen lamp having large consumption power, in addition the case of applying power voltage to the halogen lamp of the heat fixing device.
It is an object of the present invention to eliminate the above described defects
It is another object of the present invention to provide a control circuit for use in a heat fixing device capable of applying a certain power voltage automatically to the same load element without using a power supply circuit with complicated construction, even if the power voltage is changed or fluctuated.